Cryptosporidium parvum is a protozoal agent that replicates in the lining epithelial cells of the intestinal tract and biliary duct system, resulting in severe diarrhea. This is particularly true of patients infected with the human immunodeficiency virus and showing clinical manifestations of the acquired immune deficiency syndrome (AIDS). C. parvum is a common opportunistic pathogen in AIDS patients. The voluminous diarrhea, with loss of fluid and electrolytes, contributes to the death of these individuals. The undeniable importance of the immune system in controlling infection, coupled with the absence of effective therapeutic drugs, has stimulated investigation of immunological approaches to prevent and treat C. parvum infection. This proposal extends those studies by focusing on protective immune modalities will be evaluated in animal models of persistent immunotherapy protocols that resolve infection at intra-intestinal as well as extra-intestinal locations. The goal will be met by testing the following hypothesis: Protein antigens of Cryptosporidium parvum induce protective immune responses. The hypothesis will be tested by completing the following specific aims: 1. Produce Cryptosporidium parvum sporozoite and merozoite protein antigens that induce protective immune responses. 2. Characterize protective antigens obtained from specific aim 1.